Humans experience an age-related increase in the incidence of skeletal fractures and this increase may be due to a variety of factors including a decrease in bone mineral density, impaired balance and reflexes, changes in the shape and size of bones, changes in bone porosity and microarchitecture, alterations in bone mineral and organic constituents, and microdamage accumulation. The latter three factors, often referred to as "bone quality," are increasingly recognized as important determinants of fracture risk, especially for osteoporotic patients. Quantification of measures of bone quality such as microdamage accumulation and other microstructural characteristics may lead to a more accurate measure of bone strength and therefore fracture risk. Unfortunately, current technology does not allow the nondestructive and non-invasive detection of cortical bone microdamage or other measures of bone quality including microporosity. On the other hand, NMR proton spin-spin (T2) or spin-lattice (T1) relaxation time measurements and analytical processing techniques have been used to determine microstructural characteristics including porosity, pore size distribution, and permeability of various types of fluid filled porous materials with characteristic pore sizes ranging from sub-micron to sub-millimeter. We propose to develop a rapid, non-destructive and non-invasive technique based on low field pulsed NMR to detect and quantify bone microdamage and porosity and relate these measurements to bone mechanical properties. This new information may then be used in combination with or replace existing methods to more accurately assess fracture risk. The objective of the proposed research project is to develop a non-destructive technique to assess bone quality by quantifying microdamage, porosity, and pore size distribution in cortical bone. The major hypothesis to be tested in this proposal is that non-invasive NMR relaxation time measurements can be used to characterize cortical bone microdamage, porosity, and pore size distribution (measures of bone quality) and can subsequently augment or replace traditional bone mineral measurements to predict cortical bone mechanical properties. We expect our findings will allow the non-destructive and possibly in-vivo assessment of cortical bone microdamage and porosity and correlate these measures of cortical bone quality to cortical bone strength. Although this is a high-risk proposal, this new knowledge will be significant since it may ultimately lead to the development of a more accurate, less complicated, and less expensive technique to clinically assess the risk of fracture compared to currently available technology.